Electric control system



May 28, 1946. HERZ ELECTRIC common SYSTEM Filed Aug. 19, 1942 3 Sheets-Sheet 1 kgo u LQE dlfre gz l gi u I IVVIII May 28, 1946. A. HERZ ELECTRIC CONTROL SYSTEM 3 Sheets-Sheet 2 Filed Aug. 19, 1942 mvmon red hie/ may;

[ZZf 4 BY 6 s JUUJ U l lUUlli May 28, 1946. A. HERZ ELECTRIC CONTROL SYSTEM Filed Aug. 19. 1942 3 Sheets-Sheet 3 Patented May 28, 1946 Dual UH HUUH! UNITED STATES PATENT OFFICE 10 Claims.

My invention relates, generally, to electric control systems, and it has particular relation to the control of systems in which the load is intermittent or varies widely.

An object of my invention is to minimize the effect on a load circuit of a load device connected thereto that operates on a widely varying load cycle.

Another object of my invention is to automatically replace a load device adapted to be intermittently energized from a current source with an auxiliary load device of such character that the system supplied by said source is relatively insensitive to the energization or deenergization of the load device.

A further object of my invention is to automatically vary the impedance of an auxiliary load device connected across a load circuit in accordance with the flow of current to or power factor of a main load device connected thereto in such manner as to minimize the effect in said load circuit by the connection and disconnection of the main load device thereto.

Still another object of my invention is to provide a relatively high impedance in a winding by virtue of its linking a closed magnetic circuit and for reducing the impedance of said winding by energizing another winding which completely surrounds the magnetic circuit and has a relatively low impedance so that when the other winding is energized both windings together offer a relatively low impedance to the flow of current therethrough and at the same time are capable of permitting the flow of a relatively large amount of current therethrough.

Other objects of my invention will, in part, be obvious and in part appear hereinafter.

For a more complete understanding of the nature and scope of my invention reference can be had to the following detailed description taken together with the accompanying drawings in which:

Figure 1 illustrates, diagrammatically, one embodment of my invention;

Figure 2 is a view, in end elevation, of the variable impedance device employed in practicing my invention;

Figure 3 is a view, in side elevation, of the variable impedance device shown in Figure 2;

Figure 4 is a top plan view of the variable impedance device shown in Figures 2 and 3;

Figure 5 is a detail sectional view taken along the line 55 of Figure 3;

Figure 6 is a perspective view of the magnetic core structure employed in the variable impedance device shown in the preceding figures;

Figure 7 is a detail sectional view taken along the line 'I! of Figure 3; and

Figure 8 is a detail sectional view of one of the legs of the magnetic core structure shown in Figure 6.

Referring now particularly to the diagram shown in Figure 1 of the drawings, it will be observed that the reference character 10 designates a source of alternating current, such as a cycle source. The source In is arranged to be connected by switches l l and I2 to load circuit conductors l3 and It to permit energization of the same. The load circuit conductors l3 and II are arranged to energize a load device, indicated generally at l5. In this particular instance the load device [5 is one which is particularly characterized by requiring the intermittent flow of relatively large amounts of current. A particular illustration of such a device is a spot welder which requires the flow of relatively large amounts of current during brief intervals.

The load device may comprise a transformer, shown generally at l6, having a primary winding II arranged to be connected for energization to the load circuit conductors I3 and I 4. The transformer l6 includes a secondary winding 18 which, as shown, is connected to energize the spot welding electrodes I 9.

The current flow to the primary winding I! of the transformer l6 and consequently the current flow between the welding electrodes [9 can be controlled in any suitable manner, now well known to those skilled in the art. For illustrative purposes a conventional timer controller is shown at 20. The timer 2!] may comprise suitable control apparatus for permitting the flow of current to the primary winding ll in any desired manner. For example, the timer controller 20 may be arranged to permit the flow of a predetermined number of cycles or half cycles of the alternating current as conditions may warrant. The timer controller 20 may be of the electronic type or of the contactor type as will be readily understood.

Now when provision is made for energizing a load device, such as a load device l5, which requires that relatively large amounts of current flow periodically, the voltage across the load circuit conductors l3 and I, as well as across the conductors connecting the source 10 to the switches II and I2, varies more or less depending upon the stability of the system and its regulation. It often happens that other loads connected across the load circuit conductors. even when connected between the source l and the switches H and I2, are adversely affected by the application of the intermittent load applied by the device l5. This is particularly noticeable when a lighting load is connected across the load circuit conductors. When the load device I is energized, there is the tendency for the voltage across the load circuit conductors to dip or decrease and consequently the lights tend to flicker in a corresponding amount.

I propose to rectify this undesirable situation by automatically connecting across the load circuit conductors l3 and I4 an auxiliary load of such character that the regulation of the system is substantially unaffected by the energization or deenergization of the load device l5. In this manner the effective load supplied by the source I0 is more or less constant in so far as the load device I5 is concerned, depending upon the de gree of correction that is desired. It has been found that it is unnecessary to apply an auxiliary load which has exactly the same characteristics as the load device IS. The degree of correction that can be provided is determined by the economics of the situation and the amount of voltage dip which can be tolerated without being particularly objectionable. The auxiliary load device is arranged to be automatically connected across the load conductors l3 and I4 so that the same is fully energized when the current flow to the load device I5 is reduced or ceases. As soon as the load device I5 is again energized, energization of the auxiliary load is reduced to a very low value.

One manner in which the corrective action can be carried out is illustrated diagrammatically in Figure 1. The auxiliary load device comprises a variable impedance device shown generally at 22. It comprises a magnetic core structure formed by side legs 23 and 24 and end legs 25 and 26. The end legs 25 and 26 are arranged, as shown, to abut the adjacent sides of the legs 23 and 24. As will hereinafter appear the core structure is formed of laminated magnetic material. Around the leg 23 there is provided a winding 21 which is connected by conductors 29 and 30 for energization to load circuit conductors |3 and I4. When the switches I I and I2 are closed the winding 21 is energized. However, since the winding 21 links a closed magnetic circuit formed by the legs 23, 24, 25 and 26, its impedance is relatively high and a relatively small amount of current flows therethrough.

An-exciting winding 3| is provided around both legs 23 and 24 of the magnetic circuit and is connected by conductors 33 and 34 for energization to the load circuit conductors l3 and I4. As will hereinafter appear the winding 21 is formed in two sections and is distributed uniformly along the leg 23. Also, as will be set forth hereinafter the exciting winding 3| extends along the full length of both legs 23 and 24 and around the winding 21. However, for illustrative purposes the windings 21 and 3| have been illustrated as shown in Figure 1 to clarify the disclosure.

Normally the exciting winding 3| is not energized. For the purpose of energizing it switch means, shown generally at 35, are provided. As will hereinafter appear the switch means 35 are arranged to be closed when current ceases to flow to the load device [5.

When the switch means 35 are operated so as to energize the exciting winding 3|, a substantial amount of current flows therethrough in View of the fact that it does not link a closed magnetic circuit. Accordingly, the impedance of the exciting winding 3| is relatively low. The arrangement of the exciting winding 3| is such that on flow of current therethrough sufficient flux is generated by it to produce a high degree of saturation in the leg 23 of the core structure while the flux in the leg 24 is reduced. As a result, the impedance of the winding 21 is materially reduced and the current flow therethrough is correspondingly increased. The design of the variable impedance device 22 is such that the combined flow of the currents through the windings 21 and 3| produces an effect which simulates that of the load device |5 when it is energized. However, the power factor of the current flowing to the variable impedance device 22 may and preferably is substantially lower than the power factor of the current supplied to the load device l5. For example the variable impedance device 22 may have a power factor at full load of the order of 5%. Because of this, the amount of actual power taken by the variable impedance device 22 is kept at a minimum. The net result of the auxiliary load or impedance device 22 is such as to affect the regulation of the power system or feeder circuit so that voltage dips caused by power drafts taken by the welding or like load are within tolerable limits.

Any suitable form of switching means 35 can be employed provided that it is capable of satisfactorily handling the current flow to the exciting winding 3| and can be controlled so as to substantially instantaneously follow the changes in the flow of current to the load device I5.

For example, the switch means 35 may comprise a pair of ignition rectifiers 36 and 31 having control electrodes 38 and 39. As is well known the ignitrons 36 and 3'! are of the mercury vapor type and each is arranged to conduct half cycles of one polarity. By connecting two of the rectifiers 36 and 31 in the conductor 34 in reverse or back to back relation successive half cycles of the alternating current can be conducted. By controlling the excitation of the control electrodes 38 and 39, the conductivity of the rectifiers 36 and 31 is correspondingly controlled. For this purpose rectifiers 40 and 4| are provided for the rectifier 36 and the rectifiers 42 and 43 are provided for the rectifier 31. The circuit between the rectifiers 4| and 42 is controlled by means of separable contact members shown generally at 44 which are normally held in the closed position by a coil spring 45. An armature 46 is provided for cooperating with a core 41 and winding 48 for opening the contact members 44. The winding 48 is arranged to be energized from the secondary winding 49 of a transformer, the primary winding of which is a single turn and comprises the load circuit conductor l4. If desired, other means such as electronic or electric valve control means can be used in lieu of the contact members 44 and the associated operating means.

In operation, as 101 as current is being supplied to the load device l5, there is a predetermined current fiow through the secondary winding 49 of the current transformer and the armature 46 is attracted to the core 41. Contact members 44 are held in the open position and the rectifiers 36 and 31 are rendered non-conducting. No current then flows through the exciting winding 3| and only exciting current flows through the winding 21.

As soon as the current flow to the load device |5 ceases or is reduced to a predetermined value,

the armature 46 is released and contact members 44 are closed. The circuit between the rectifiers 4| and 42 is then closed and the rectifiers 36 and 31 are then rendered conducting during successive half cycles as long as the contact members 44 remain in the closed position. The rectifiers 36 and 3'! then conduct successive half cycles of the alternating current and the exciting winding 3| is energized. As previously described the current flow through the exciting winding 3| is suflicient to increase the saturation of the magnetic core structure and consequently the impedance of the winding 21 is materially reduced. The auxiliary load or variable impedance device 22 then has much the same effect on the power system as does the load device I5. Consequently, the range in variation of voltage across the load circuit conductors caused by intermittent energization of the load device I5 is materially reduced. The extent to which it is reduced will of course depend, as previously set forth, upon the economics of the situation and the degree of compensation that is required or the variation in voltage which can be tolerated.

The details of construction that are desirable in the impedance device 22 are shown in Figures 2 through 8 of the drawings to which reference will now be had.

As shown more clearly in Figure 6 of the drawings the magnetic core structure is formed by the elongated legs 23 and 24 of laminated magnetic material and members or legs 25 and 26 of the same material. The butt joints between the juxtaposed surfaces of the legs 23, 24, 25 and 26 will be noted. This butt joint construction is provided so as to permit varying the effectiveness of the magnetic circuit by varying the air gaps between the abutting members by means which will be described hereinafter.

It will be observed in Figures 4 and 5 that the winding 21 is formed in two sections which are identified as 210 and 21b. This is for cooling purposes. These sections or coils 21a and 21b are concentrically arranged about the leg 23 and extend the full length thereof between the end legs 25 and 26 of the magnetic circuit.

The exciting coil 3| is wound generally in the form of a D and, as shown, it surrounds the coils 21a and 21b and also both legs 23 and 24 of the magnetic circuit. The winding 3| is coextensive with the windings 21a and 21b.

As shown in Figure 8 of the drawings suitable clamp members 53 are provided along the leg 23 and clamp bolts 54 serve to hold them and thereby the laminations making up the leg 23 in place. The laminations making up the legs 24, 25 and 26 are held together by through bolts, the apertures of which are shown in Figure 6.

Generally L-shaped clamp members 56 and 51 are provided at the top and bottom of the core structure as illustrated in Figures 2, 3 and 4 of the drawings for the purpose of holding the various parts in rigid spaced re. .ition. The upstanding flanges of the L-shaped members 56 are spaced apart by a wood spacer Cd through which clamp bolts 59 extend. The spacer 58 can be extended lengthwise beyond the ends of the clamp members 56 to provide a means for supporting or rigidly locating the entire assembly in a metallic tank if desired.

The lower L-shaped clamp members 51 are spaced apart by a wood block 60 and clamped in place by bolts 6|. Feet 62 extend outwardly from the depending portions of the clamp members 51 to provide a footing for the device as it is mounted on the bottom of a tank. Longitudinally extending bolts 63 serve to interconnect the parallel fiat portions of the clamp members 56 and 51.

As previously indicated the variable impedance device is intended to be mounted in a tank and to be covered with a suitable insulating and/or cooling liquid as is conventional in transformer practice. In order to facilitate circulation of the insulating liquid the flat portions of the clamp members 56 and 51 are provided with large openings 64, Figure 4, some of which register with the spaces between the various windings mounted on the core structure.

With a view to providing for adjusting the air gaps between the legs making up the main leg core structure adjusting screws 61 are provided in yokes 68 which extend between the upwardly and downwardly extending portions of the clamp members 56 and 51 respectively. By tightening or loosening the adjusting screws 61 it is possible to decrease or increase the air gaps between the juxtaposed surfaces of the legs making up the magnetic core structure. If desired, non-metallic spacer shims can be provided between these juxtaposed surfaces to increase the rigidit of the magnetic core structure.

Since various changes can be made in the foregoing system and construction without departing from the spirit and scope of the present invention, it is understood that the subject matter set forth hereinbefore and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. The combination, with a. source of alternating current and a load device adapted to be energized therefrom by intermittent flow of current thereto, of a winding connected to be energized in parallel with said load device, a closed magnetic circuit linking said winding whereby the same offers a relatively high impedance to flow of current therethrough, an alternating current exciting winding surrounding said magnetic circuit for controlling the degree of saturation thereof, ignitron contactor means for selectively connecting said exciting winding for energization to said source of alternating current, and a current responsive relay for controlling said ignitron contactor means in accordance with the flow of current to said load device for varying the impedance of the first mentioned winding so that it is relatively high when said current flows to said load device and is relatively low when said current flow is reduced.

2. The combination, with a source of alternating current and a load device adapted to be energized therefrom by intermittent flow of current thereto, of a substantially closed core of magnetic material comprising two side legs, a reactance winding on one of said side legs connected to be energized from said source in parallel with said load device and cooperating with said core to offer a relatively high impedance to flow of current therethrough, an alternating current exciting winding disposed on said core and surrounding both of said side legs and said reactance winding in such manner that it offers a relatively low impedance to flow of current therethrough, and means comprising two ignitron rectifiers connected in inverse parallel relation for controlling the connection of said exciting winding to said source of alternating current in accordance with the flow of current to said load device for varying the impedance of said reactance winding so that it is relatively high when said current flows I lUUIlI to said load device and is correspondingly low when said current flow is reduced with the result that the range of variation of the volt amperes supplied by said source is minimized with respect to the range of variation of volt amperes supplied to said load device alone.

3. The combination, with a source of alternating current and a main load device adapted to be energized intermittently therefrom, of an auxiliary load device connected to be energized from said source, said auxiliary load device comprising a reactance type of energy dissipating means of relatively low power factor, ignitron contactor means for controlling the energization of said auxiliary load device, and a current responsive relay for controlling said ignitron contactor means in accordance with the flow of current to said main load device for varying the reactance of said auxiliary load device so that it is relatively high when said current flows to said main load device and is relatively low when said current flow is reduced.

4. The combination, with a source of alternating current and a main load device adapted to be energized therefrom by intermittent flow of current thereto, of an artificial load device connected to be energized from said source, said artificial load device comprising a reactance winding through which substantially all of the energy of the artificial load is adapted to be dissipated, and means comprising two ignitron rectifiers connected in inverse parallel relation for controlling the reactance of said reactance winding in accordance with the flow of current to said main load device whereby the reactance of said reactance winding is relatively high when said current flows to said main load device and is correspondingly low when said current flow is reduced, with the result that the range of variation of the volt amperes supplied by said source is minimized with respect to the range of variation of volt amperes supplied to said main load device alone.

5. The combination, with a source of alternating current and a load device adapted to be energized therefrom by intermittent flow of current thereto, of a substantially closed core of magnetic material comprising two side legs, a reactance winding on one of said side legs connected to be energized from said source in parallel with said load device and cooperating with said core to offer a relatively high impedance to flow of current therethrough, an alternating current exciting windin disposed on said core and surrounding both of said side legs in such manner that it oiTers a relatively low impedance to flow of current therethrough, ignitron contactor means for selectively connecting said exciting winding for energization to said source of alternating current, and a current responsive relay for controlling said ignitron contactor means in accordance with the flow of current to said load device for varying the impedance of the first mentioned winding so that it is relatively high when said current flows to said load device and is relatively low when said current flow is reduced.

6. The combination, with a source of alternating current and a load device adapted to be energized therefrom by intermittent flow of current thereto, of a substantially closed core of magnetic material comprising two side legs, a reactance winding on one of said side legs connected to be energized from said source in parallel with said load device and cooperating with said core to offer a relatively high impedance to flow of current therethrough, an alternating current exciting winding disposed on said core and surrounding both of said legs in such manner that it offers a relatively low impedance to flow of current therethrough, and electronic switch means of the ignitron type for controlling the connection of said alternating current exciting winding to said source of alternating current in accordance with the flow of current to said load device for varying the impedance of said reactance winding so that it is relatively high when said current flows to said load device and is correspondingly low when said current flow is reduced, with the result that the range of variation of the volt amperes supplied by said source is minimized with respect to the range of variation of volt amperes supplied to said load device alone.

7. The combination, with a source of alternating current and a load device adapted to be energized therefrom by intermittent flow of current thereto, of a substantially closed core of magnetic material comprising two side legs, a reactance winding on one of said side legs connected to be energized from said source in parallel with said load device and cooperating with said core to offer a relatively high impedance to flow of current therethrough, an alternating current exciting winding disposed on said core and surrounding both of said legs in such manner that it ofiers a relatively low impedance to flow of current therethrough, and means for controlling the connection of said alternating current exciting winding to said source of alternating current in accordance with the flow of current to said load device for varying the impedance of said reactance winding so that it is relatively high when said current flows to said load device and. is correspondingly low when said current is reduced, with the result that the range of variation of the volt amperes supplied by said source is minimized with respect to the range of variation of volt amperes supplied to said load device alone.

8. The combination, with a source of alternating current and a load device adapted to be energized therefrom by intermittent flow of current thereto, of a substantially closed core of magnetic material comprising two side legs, a reactance winding on said core connected to be energized from said source in parallel with said load device, an alternating current exciting winding surrounding both side legs of said core whereby both side legs function as an open-ended core for said alternating current exciting winding, and means for controlling the energization of said alternating current exciting winding from said source of alternating current in accordance with the flow of current to said load device whereby to vary the impedance of said reactance winding so that this impedance is relatively high when there is a large flow of current to said load device and is relatively low when said current flow is reduced.

9. The combination, with a source of alternating current and a load device adapted to be energized therefrom by intermittent flow of current thereto, of a substantially closed core of magnetic material comprising two side legs, a reactance winding on said core connected to be energized from said source in parallel with said load device, an alternating current exciting winding surrounding both side legs of said core whereby both side legs function as an open-ended core for said alternating current exciting winding, and electronic switch means for controlling the connection of said alternating current exciting winding to said source of alternating current.

10. The combination with a source of alternating current and a main load device adapted to be energized therefrom on a varying load cycle, of an auxiliary load device adapted to be energized from said source of alternating current, said auxiliary load device comprising a static core structure, a static reactance winding on said core structure and a static exciting winding on said core structure, said reactance winding being connected to be energized with alternating current from said source whereby to create alternating current reactance flux in said core structure, and automatic control means responsive to said main load device and operative to transmit alternating current from said source through said exciting winding whereby to create alternating current control flux in said core structure which is operative to control said a1- ternating current reactance flux in said core structure and thereby vary the reactance of said reactance winding.

ALFRED HERZ. 

